Dev is saying a large drop of codes are going out tomorrow, and that if you've signed up you have a very good chance at receiving a code to play. The codes have been being sent out around 8AM PST the last few days, so check then for codes. They've been being eaten up in mere minutes though. If you check that dev's twitter feed, he has also confirmed multi-monitor support as well :)

If you don't happen to get a code tomorrow through email, or if you didn't sign up check out this Reddit thread for key courses (and even check the SimCity subreddit for other posts on key sources), and also check the NVIDIA promo site here, which is where I got mine.

edit- This guy has been giving codes out every so often for the past few hours. Just keep checking his feed. Extensions or addons for FireFox and Chrome work wonders too :0